Golf ball

ABSTRACT

A golf ball includes, as a composing element, a hot-molded product obtained from a rubber composition which includes a main rubber containing 10 to 90 mass % of a polybutadiene, an unsaturated carboxylic acid and/or a metal salt thereof, and an organic peroxide. The polybutadiene has 60% or more of cis-1,4-bonds. Further, letting a Mooney viscosity (ML 1+4 (100° C.)) of the polybutadiene be ML and a viscosity of a toluene solution containing 5 mass % of the polybutadiene at 25° C. be η(mPa·s), ML and η satisfy a relationship of η≧20×ML−600.

CROSS REFERENCE TO RELATED APPLICATION

This application is an application filed under 35 U.S.C. §111(a)claiming benefit pursuant to 35 U.S.C §119(e)(i) of the filing date ofthe Provisional Application No. 60/300,861 filed on Jun. 27, 2001pursuant to 35 U.S.C. §111(b).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a golf ball including a molded productobtained from a polybutadiene having a linearity of butadiene rubbermolecules, and exhibiting very high resilience.

2. Prior Art

Conventionally, to give excellent resilience to a golf ball, variousattempts have been made to improve the composition of a polybutadieneused as a main rubber for the golf ball.

For example, Japanese Patent Laid-open No. Sho 62-89750 has proposed arubber composition for a solid golf ball, which contains, as a mainrubber, a polybutadiene having a Mooney viscosity ranging from 70 to 100and synthesized by using an Ni or Co catalyst and a polybutadiene havinga Mooney viscosity ranging from 30 to 90 and synthesized by using alantern based catalyst or a polybutadiene having a Mooney viscosityranging from 20 to 50 and synthesized by using an Ni or Co catalyst.

The above-described golf ball, however, has been further required to beimproved in terms of resilience of the ball.

Japanese Patent Laid-open No. Hei 2-268778 has proposed a golf ball,which is produced from a rubber composition containing a polybutadienehaving a Mooney viscosity of less than 50 and synthesized by using agroup VIII element catalyst and a polybutadiene having a Mooneyviscosity of less than 50 and synthesized by using a lanthanidecatalyst. The golf ball thus obtained, however, is poor in resilience.

Japanese Patent Laid-open No. Hei 11-70187 has proposed a multi-piecesolid golf ball including an intermediate layer made from apolybutadiene having a low Mooney viscosity; Japanese Patent Laid-openNo. Hei 11-319148 has proposed a solid golf ball produced from a rubbercomposition containing a polybutadiene having a Mooney viscosity rangingfrom 50 to 60 and synthesized by using an Ni or Co catalyst and apolybutadiene having a Mooney viscosity ranging from 20 to 90 andsynthesized by using lanthanoid based catalyst; Japanese PatentLaid-open No. Hei 11-164912 has proposed a solid golf ball produced froma rubber composition in which the amount of 1,2-vinyl bonds is in arange of 2.0% or less and a ratio (Mw/Mn) of a weight-average molecularweight to a number-average molecular weight is in a range of 3.5 orless; Japanese Patent Laid-open No. Sho 63-275356 has proposed a golfball produced from a rubber composition containing a polybutadienehaving a high Mooney viscosity; and Japanese Patent Laid-open No. Hei3-151985 has proposed a golf ball produced from a rubber compositioncontaining a polybutadiene having a high number-average molecular weightand a polybutadiene having a low number-average molecular weight. Eachof these golf balls, however, is insufficient in resilience of the ball.

SUMMARY OF THE INVENTION

In view of the foregoing, the present inventor has earnestly examinedand found that a golf ball including, as a composing element, ahot-molded product obtained from a rubber composition which includes amain rubber containing 10 to 90 mass % of a polybutadiene (a), anunsaturated carboxylic acid and/or a metal salt thereof, and an organicperoxide, wherein the polybutadiene has 60% or more of cis-1,4-bonds,and letting a Mooney viscosity (ML₁₊₄(100° C.)) of the polybutadiene beML and a viscosity of a toluene solution containing 5 mass % of thepolybutadiene at 25° C. be (mPa·s), ML and η satisfy a relationship ofη≧20×ML−600, is advantageous in that a very excellent hot-molded productcan be obtained by a synergism effect of the polybutadiene having a veryhigh linearity of rubber molecules and the other components, and that agolf ball having such a hot-molded product has very excellentresilience, thereby increasing the carry of the ball. On the basis ofthe above knowledge, the present invention has been accomplished.

Accordingly, the present invention provides the following golf balls:

(1) A golf ball including, as a composing element, a hot-molded productobtained from a rubber composition, the rubber composition including:

a main rubber containing 10 to 90 mass % of a polybutadiene (a);

an unsaturated carboxylic acid and/or a metal salt thereof; and

an organic peroxide;

wherein the polybutadiene has 60% or more of cis-1,4-bonds; and

letting a Mooney viscosity (ML₁₊₄(100° C.)) of the polybutadiene be MLand a viscosity of a toluene solution containing 5 mass % of thepolybutadiene at 25° C. be 1(mPa·s), Ml and η satisfy a relationship ofη≧20×ML−600.

(2) A golf ball according to claim 1, wherein the polybutadienecomponent (a) is synthesized by using a rare earth element basedcatalyst.

(3) A golf ball according to claim 1 or 2, wherein the polybutadienecomponent (a) is synthesized by using a rare earth element basedcatalyst, and is then reacted with a terminal denaturant.

(4) A golf ball according to any one of claims 1 to 3, wherein the mainrubber contains, in addition to the polybutadiene component (a), 90 to10 mass % of a polybutadiene (b) having a Mooney viscosity of 55 orless.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail. A golfball of the present invention includes a hot-molded product obtainedfrom a rubber composition. The rubber composition includes a main rubbercontaining 10 to 90 mass % of a polybutadiene (a), wherein thepolybutadiene has 60% or more of cis-1,4-bonds, and letting a Mooneyviscosity (ML₁₊₄(100° C.)) of the polybutadiene be ML and a viscosity ofa toluene solution containing 5 mass % of the polybutadiene at 25° C. beη(mPa·s), ML and η satisfy a relationship of η≧20×ML−600.

The polybutadiene component (a) is required to have the cis-1,4-bonds inan amount of 60% or more, preferably, 80% or more, more preferably, 90%or more, most preferably, 95% or more. If the amount of thecis-1,4-bonds is excessively small, the resilience is reduced.

The polybutadiene component (a) of the present invention is required tobe specified such that letting a Mooney viscosity (ML₁₊₄(100° C.)) ofthe polybutadiene be ML and a viscosity of a toluene solution containing5 mass % of the polybutadiene at 25° C. be η(mPa·s), ML and η satisfy arelationship of η≧20×ML−600, preferably, η≧20×ML−580, more preferably,η≧20×ML−560, most preferably, η≧20×ML−540. Since the polybutadiene withthe viscosities η and ML optimized has a high linearity of polybutadienemolecules, it can give very excellent resilience to a molded-product.

The polybutadiene component (a) of the present invention may be furtherspecified such that the upper limit of the viscosity η be in a range ofη≦20×ML−100, preferably, η≦20×ML−150, more preferably, η≦20×ML−200, mostpreferably, η≦20×ML−250.

The viscosity η(mPa·s) of a toluene solution containing 5 mass % of apolybutadiene at 25° C. used herein is determined by a manner ofdissolving 2.28 g of the polybutadiene to be measured in 50 ml oftoluene, and measuring a viscosity of the toluene solution under acondition with 25° C. using a viscometer constituting standard solution(JIS Z8809) by a specific viscometer.

The Mooney viscosity used herein is an industrial index of viscositymeasured by a Mooney viscometer which is one kind of a rotaryplastimeter under JIS-K6300. The Mooney viscosity is expressed inML₁₊₄(100° C.), where M indicates the Mooney viscosity, L indicates alarge rotor (L-type) of the plastimeter, “(1+4)” indicates that apre-heating time is one minutes and a rotational time of the rotor isfour minutes, and “100° C.” indicates a measurement temperature.

The Mooney viscosity [ML₁₊₄(100° C.)] of the polybutadiene component (a)is required to be in a range of 20 or more, preferably, 30 or more, morepreferably, 40 or more, most preferably, 50 or more, with the upperlimit being in a range of 80 or less, preferably, 70 or less, morepreferably, 65 or less, most preferably, 60 or less.

The polybutadiene component (a) of the present invention is required tobe synthesized by using a rare earth element based catalyst.

As the rare earth element based catalyst, there can be used a known typesuch as lantern series rare earth element compound, an organic aluminumcompound, alumoxane, a halogen containing compound, or a combinationthereof with a Lewis base.

Examples of the lantern series rare earth element compounds may includea halide, a carboxylate, an alcoholate, a thioalcoholate, and an amideof a metal having an atomic number of 57 to 71.

As the organic aluminum compound, there can be used a compoundexpressed, for example, by AlR₁R²R³ (R¹, R² and R³ may be identical toeach other or different from each other, and each of R¹, R² and R³ is aresidual hydrocarbon group having the hydrogen or carbon number of 1 to8).

As the alumoxane, there is preferably used a compound having a structureexpressed by the following chemical formula (1) or (2):

In each chemical formula, R⁴ is a hydrocarbon group containing carbonatoms of the carbon number of 1 to 20, and n is an integer of 2 or more.

In addition, an associated body of the alumoxane indicated by “FineChemical, 23, (9), 5 (1994)”, “J. Am. Chem. Soc., 115, 4971 (1993)”, or“J. Am, Chem. Soc., 117, 6465 (1995)” may be used.

As the halogen containing compound, there can be used an aluminum halideexpressed by AlX_(n)R_(3−n) (X is a halogen, R is a residual hydrocarbongroup having the carbon number of 1 to 20, for example, an alkyl group,aryl base, or aralkyl base, and n is 1, 1.5, 2 or 3), a strontium halidesuch as Me₃SrCl, Me₂SrCl₂, MeSrHCl₂, MeSrCl₃, or a metal halide such assilicon tetrachloride, tin tetrachloride, or titanium tetrachloride.

The Lewis base can be used for complexing the lantern series rare earthelement compound. For example, acethyl acetone or ketone alcohol can beused as the Lewis base.

According to present invention, particularly, the use of a neodymiumbase catalyst using a neodymium compound as the lantern series rareearth element compound advantageously allows production of apolybutadiene containing a large amount of the cis-1,4-bonds and a smallamount of the 1,2-vinyl bonds with an excellent polymerization activity.The concrete example of the rare earth element based catalyst has beendescribed in Japanese Patent Laid-open No. Hei 11-35633.

In the case of polymerization of butadiene monomers under a rare earthelement catalyst, a solvent may be used, or any solvent may be not used.In the latter case, butadiene monomers may be subjected to bulkpolymerization or a vapor-phase polymerization. The polymerizationtemperature may be in a range of 30 to 150° C., preferably, 10 to 100°C.

The polybutadiene component (b) of the present invention may be obtainedby polymerization using the rare earth based catalyst, followed byreaction of active terminals of the polymer with a terminal denaturant.

As the terminal denaturants, there can be used the following knowncompounds (1) to (6):

(1) A halogenated organic metal compound, a halogenated metal compound,or an organic metal compound expressed by R⁵ _(n)M′X_(4−n), M′X₄, M′X₃,R⁵ _(n)M′(—R⁶—COOR⁷)_(4−n), or R⁵ _(n)M′(—R⁶—CoR⁷)_(4−n), (in thechemical formula, R⁵ and R⁶ may be identical to each other or differentfrom each other, and each of R⁵ and R⁶ is a hydrocarbon group containingcarbon atoms of the carbon number of 1 to 20; R⁷ is a hydrocarbon groupcontaining carbon atoms of the carbon number of 1 to 20, which maycontain a carbonyl group or ester group at a side chain; M′ is a tinatom, silicon atom, germanium atom, or phosphorus atom; X is a halogenatom; and n is 0 or an integer selected from 1 to 3).

(2) A heterocumulene compound containing, in molecules, Y═C═Z bonds (inthe formula, Y is a carbon atom, oxygen atom, nitrogen atom, or sulfuratom; Z is an oxygen atom, nitrogen atom, or sulfur atom).

(3) A hetero-tricyclic compound containing, in molecules, bondsexpressed by the following chemical formula:

In the chemical formula, Y is an oxygen atom, nitrogen atom, or sulfuratom.

(4) A halogenated isocyano compound.

(5) R⁸—(COOH)_(m), R⁹(COX)_(m), R¹⁰—(COO—R¹¹), R¹²—OCOO—R¹³,R¹⁴—(COOCO—R¹⁵)_(m), or a carboxylic acid, an acid halide, an estercompound, a carbonic ester compound, or an acid anhydride, which isexpressed by the following chemical formula:

In the formula, R⁸ to R¹⁶ may be identical to each other or differentfrom each other, and each of R⁸ to R¹⁶ is a hydrocarbon group containingcarbon atoms of the carbon number of 1 to 50, X is a halogen atom, and mis an integer selected from 1 to 5.

(6) R¹⁷ ₁, M″(OCOR¹⁸)⁴⁻¹, R¹⁹ ₁M″(OCO—R²⁰—COR²¹)⁴⁻¹, or a metal salt ofa carboxylic acid expressed by the following chemical formula:

In the chemical formula, R¹⁷ to R²³ may be identical to each other ordifferent from each other, and each of R¹⁷ to R²³ is a hydrocarbon groupcontaining carbon atoms of the carbon number of 1 to 20, M″ is a tinatom, silicon atom, or germanium atom, 1 is 0 or an integer selectedfrom 1 to 3.

A concrete example of the terminal denaturant shown in each of the aboveitems (1) to (6) and a method of allowing the terminal denaturant toreact with active terminals of a polymer have been disclosed, forexample, in Japanese Patent Laid-open Nos. Hei 11-35633 and Hei7-268132.

The main rubber is required to contain the polybutadiene component (a)in an amount of 10 mass % or more, preferably, 20 mass % or more, morepreferably, 30 mass % or more, most preferably, 40 mass % or more, withthe upper limit being in a range of 90 mass % or less, preferably, 80mass % or less, more preferably, 70 mass % or less, most preferably, 60mass % or less. If the content of the polybutadiene component (a) is outof the above range, the resilience of the molded product is reduced,thereby failing achieve the function and effect of the presentinvention.

The polubutadiene component (b) of the main rubber of the presentinvention is not an essential component of the rubber composition of thepresent invention and may be added in such a range as not to obstructthe object of the present invention, as needed. Examples of thepolybutadiene component (b) may include polubutadiene rubber (BR),styrene-butadiene rubber (SBR), natural rubber, polyisoprene rubber, andethylene-propylene-diene rubber (EPDR). These materials may be addedsingly or in combination of two kinds or more. Preferably, to improvethe resilience, and the moldability such as workability in extrusion ofthe rubber composition, the polybutadiene component (b) may be apolybutadiene other than the polybutadiene component (a), wherein theMooney viscosity of the polybutadiene may be in a range of 55 or less,preferably, 50 or less, more preferably, 47 or less, most preferably, 45or less, with the lower limit being in a range of 10 or more,preferably, 20 or more, more preferably, 25 or more, most preferably, 30or more.

The polybutadiene component (b) is recommended to be synthesized byusing a group VIII element catalyst, for example, a nickel basedcatalyst or a cobalt based catalyst.

Examples of the nickel based catalysts may include a one-component typesuch as nickel diatomaceous earth; a two-component type such asRaney-nickel/titanium tetrachloride; and a three-component type such asa nickel compound/organic metal/boron trifluoride etherate. Examples ofnickel compounds may include reduced nickel with carrier, Raney-nickel,nickel oxide, nickel carboxylate, and a complex salt of organic nickel.Examples of the organic metals may include a trialkyl aluminum such astriethyl aluminum, tri-n-propyl aluminum, tri-isobutyl aluminum, ortri-n-hexyl aluminum; an alkyl lithium such as n-butyl lithium,sec-butyl lithium, tert-butyl lithium, or 1,4-dibutane lithium; and adialkyl zinc such as diethyl zinc or dibutyl zinc.

Examples of the cobalt based catalysts may include, as cobalt andcompounds thereof, Raney-cobalt, cobalt chloride, cobalt bromide, cobaltiodide, cobalt oxide, cobalt sulfate, cobalt carbonate, cobaltphosphate, cobalt phthalate, cobalt carbonyl, cobalt acetylacetonate,cobalt diethyl dithiocarbamate, cobalt anilinium nitrite, and cobaltdinitrosyl chloride. In particular, each of these compounds ispreferably combined with a dialkyl aluminum monochloride such as diethylaluminum monochloride or diisobutyl aluminum monochloride, a trialkylaluminum such as triethyl aluminum, tri-n-propyl aluminum, triisobutylaluminum or tri-n-hexyl aluminum, an aluminum alkyl sesquichloride suchas ethyl aluminum sesquichloride, or aluminum chloride.

The polymerization of butadiene monomers by using the above group VIIIelement based catalyst, particularly, a nickel or cobalt based catalystcan be generally performed by continuously charging the butadienemonomers and the catalyst, together with a solvent, in a reactionchamber, and subjecting them to reaction by suitably selecting areaction temperature in a range of 5 to 60° C. and a reaction pressurein a range of atmospheric pressure to 70 and several atm so as to obtainthe above-described Mooney viscosity.

In the case of adding another polybutadiene, particularly, thepolybutadiene component (b) to the polybutadiene component (a) forforming the main rubber, the added amount of the polybutadiene may be ina range of 90 mass % or less, preferably, 80 mass % or less, morepreferably, 70 mass % or less, most preferably, 60 mass % or less, withthe lower limit being in a range of 10 mass % or more, preferably, 20mass % or more, more preferably, 30 mass % or more, most preferably, 40mass % or more.

The rubber composition of the present invention is obtained by adding anunsaturated carboxylic acid and/or a metal salt thereof and an organicperoxide as essential components to the main rubber containing aspecific amount of the polybutadiene component (a). A hot-molded productobtained from such a rubber composition is excellent in resilience, witha result that a golf ball including the hot-molded product becomesexcellent in resilience.

Examples of the unsaturated carboxylic acids may include acrylic acid,metacrylic acid, maleic acid, fumaric acid. In particular, acrylic acidand metacrylic acid are preferably used.

Examples of the metal salts of unsaturated carboxylic acids may includezinc salts and magnesium salts of unsaturated aliphatic acids, forexample, zinc metacrylate and zinc acrylate. In particular, zincacrylate is preferably used.

The content of the unsaturated carboxylic acid and/or metal salt thereofmay be set, on the basis of 100 parts by mass of the main rubber, in arange of 10 parts by mass or more, preferably, 15 parts by mass or more,more preferably, 20 parts by mass or more, with the upper limit being ina range of 60 parts by mass or less, preferably, 50 parts by mass orless, more preferably, 45 parts by mass or less, most preferably, 40parts by mass or less. If the content is excessively small, theresilience is reduced, and if excessively large, the golf ball becomesexcessively hard, which may make player's feeling of hitting of the golfball undesirable.

As the organic peroxide, there can be used a commercial product such as“Percumyl D” (sold by NOF CORPORATION), “Perhexa 3M” (sold by NOFCORPORATION), “Luperco 231XL” (sold by Elf Atochem Japan). Two kinds ormore organic peroxides may be used in combination as needed.

The content of the organic peroxide may be set, on the basis of 100parts by mass of the main rubber containing the polybutadiene component(a) as an essential component, in a range of 0.1 part by mass or more,preferably, 0.3 part by mass or more, more preferably, 0.5 part by massor more, most preferably, 0.7 part by mass or more, with the upper limitbeing in a range of 5 parts by mass or less, preferably, 4 parts by massor less, more preferably, 3 parts by mass or less, most preferably, 2parts by mass or less. If the content is excessively large or small, theresilience, player's feeling of hitting the golf ball, and durabilitymay be degraded.

In addition to the above-described essential components, an inorganicfiller can be added to the rubber composition of the present inventionfor adjusting the specific gravity, as needed. Examples of the inorganicfillers may include zinc oxide, barium sulfate, and calcium carbonate.In order to obtain a suitable weight and desirable resilience, thecontent of the inorganic filler may be set, on the basis of 100 parts bymass of the main rubber containing the polybutadiene component (a) as anessential component, in a range of 1 part by mass or more, preferably, 3parts by mass or more, more preferably, 5 parts by mass or more, mostpreferably, 7 parts by mass or more, with the upper limit being in arange of 130 parts by mass or less, preferably, 50 parts by mass orless, more preferably, 45 parts by mass or less, most preferably, 40parts by mass or less.

An antioxidant may be further added to the rubber composition of thepresent invention, as needed. As the antioxidant, there can be used acommercial product such as “NOCRAC NS-6, NS-30” (sold by Ouchi-SinkoChemical Industrial Co., Ltd.), or “Yoshinox 425” (YoshitomiPharmaceutical Co., Ltd.). In order to obtain desirable resilience anddurability, the content of the antioxidant may be set, on the basis of100 parts by mass of the main rubber containing the polybutadienecomponent (a) as an essential component, in a range of 0 part by mass ormore, preferably, 0.05 part by mass or more, more preferably, 0.1 partby mass or more, most preferably, 0.2 part by mass or more, with theupper limit being in a range of 3 parts by mass or less, preferably, 2parts by mass or less, more preferably, 1 part by mass or less, mostpreferably, 0.5 part by mass or less.

The rubber composition of the present invention can further contain anorganic sulfur compound. Examples of the organic sulfur compounds mayinclude thiophenol, thionaphthol, halogenated thiophenol, or metal saltsthereof, more concretely, zinc salts of pentachlorothiophenol,pentafluorothiophenol, pentabromothiophenol, and parachlorothiophenol;and diphenyl polysulfide, dibenzil polysulfide, dibenzoil polysulfide,dibenzothiazoil polysulfide, and dithiobenzoil polysulfide, each ofwhich has the sulfur number of 2 to 4. In particular, a zinc salt ofpentachlorothiophenol or diphenyl disulfide is preferably used. Thecontent of the organic sulfur compound may be set, on the basis of 100parts by mass of the main rubber obtained by mixing the polybutadienecomponent (a) as an essential component with the polybutadiene component(b) at a specific mixing ratio, in a range of 0.1 part by mass or more,preferably, 0.2 part by mass or more, more preferably, 0.5 part by massor more, with the upper limit being in a range of 5 parts by mass orless, preferably, 4 parts by mass or less, more preferably, 3 parts bymass or less, most preferably, 2 parts by mass or less.

The hot-molded product of the present invention can be obtained byvulcanizing and heating the above-described rubber composition by aknown process. For example, a vulcanizing temperature may be set in arange of 100 to 200° C., and a vulcanizing time be set in a range of 10to 40 min.

According to the present invention, the hardness of the hot-moldedproduct can be suitably adjusted in accordance with the usage form (tobe described later) of a golf ball, and is not particularly limited. Forexample, the sectional hardness of the hot-molded product may be uniformfrom the center to the surface of the molded-product, or a difference insectional hardness may be present between the center and the surface ofthe molded-product.

Irrespective of the form of the golf ball, a flexural amount of thehot-molded product, measured by applying a load of 980 N (100 kg)thereto, may be in a range of 2.0 mm or more, preferably, 2.5 mm ormore, more preferably, 2.8 mm or more, most preferably, 3.2 mm or more,with the upper limit being in a range of 6.0 mm or less, preferably, 5.5mm or less, more preferably, 5.0 mm or less, most preferably, 4.5 mm orless. If the flexural amount, that is, the deformed amount isexcessively small, player's feeling of hitting the golf ball becomesworse, and particularly, the spin of the ball becomes excessively highat the time of long-shot with a driver when the ball is liable to belargely deformed, to reduce the carry of the ball, and if the deformedamount is excessively large, that is, if the golf ball becomesexcessively soft, player's feeling of hitting the ball becomes dull, thecarry of the ball is reduced because of insufficient resilience, anddurability against cracking due to repeated hitting may become worse.

The golf ball of the present invention is characterized by including theabove hot-molded product as a composing element, and the form of theball is not particularly limited. To be more specific, the golf ball ofthe present invention may be any of a one-piece golf ball in which thehot-molded product is directly applied to the golf ball, a two-piecesolid golf ball in which the hot-molded product is used as a solid coreon the surface of which a cover is formed, a multi-piece solid golf ballhaving three-pieces or more in which the hot-molded product is used as asolid core on the surface of which two or more cover layers are formed,and a bobbin type golf ball in which the hot-molded product is used as acenter core. In particular, from the viewpoint of making effective useof the hot-molded product to improve the moldability in extrusion of therubber composition and give excellent resilience to the ball, the golfball of the present invention is preferably used in the form of atwo-piece solid golf ball or a multi-piece solid golf ball.

According to the present invention, in the case of using the hot-moldedproduct as a solid core, the diameter of the solid core may be in arange of 30.0 mm or more, preferably, 32.0 mm or more, more preferably,35.0 mm or more, most preferably, 37.0 mm or more, with the upper limitbeing in a range of 41.0 mm or less, preferably, 40.5 mm or less, morepreferably, 40.0 mm or less, most preferably, 39.5 mm or less. Inparticular, the diameter of the solid core used for a two-piece solidgolf ball may be in a range of 37.0 mm or more, preferably, 37.5 mm ormore, more preferably, 38.0 mm or more, most preferably, 38.5 mm ormore, with the upper limit being in a range of 41.0 mm or less,preferably, 40.5 mm or less, more preferably, 40.0 mm or less; and thediameter of the solid core used for a three-piece solid golf ball may bein a range of 30.0 mm or less, preferably, 32.0 mm or less, morepreferably, 34.0 mm or more, most preferably, 35.0 mm or more, with theupper limit being in a range of 40.0 mm or less, preferably, 39.5 mm orless, more preferably, 39.0 mm or less.

The specific gravity of the solid core may be in a range of 0.9 or more,preferably, 1.0 or more, more preferably, 1.1 or more, with the upperlimit being in a range of 1.4 or less, preferably, 1.3 or less, morepreferably, 1.2 or less.

In the case where the golf ball of the present invention is applied to atwo-piece solid golf ball or a multi-piece solid golf ball, the golfball can be produced by putting a solid core formed of the hot-moldedproduct, and injecting-molding or press-molding a known cover material,or a known cover material and a known intermediate layer material on thesolid core.

As a main material of each of the cover material and intermediate layermaterial, there may be used a thermoplastic or thermosettingpolyurethane based elastomer, a polyester based elastomer, an ionomerresin, a polyolefine based elastomer, or a mixture thereof. Thesematerials may be used singly or in combination of two kinds or more. Inparticular, the thermoplastic polyurethane elastomer or ionomer resin ispreferably used.

As the thermoplastic polyurethane based elastomer, there can be used acommercial product such as an elastomer containing aliphatic or aromaticdiisocyanate, for example, “Pandex T7298, T7295, T7890, TR3080, T8295,or T8290” (sold by DIC-Bayer Polymer Co., Ltd.). As the ionomer resin,there can be used a commercial product such as “Surlyn 6320, or 8120”(sold by Du Pont DE NEMOURS & COMPANY, USA), or “Himilan 1706, 1605,1855, 1601, or 1557” (sold by Du Pont-Mitsui Polychemicals Co., Ltd.).

Another polymer such as a thermoplastic elastomer other than thatdescribed above may be added, as an arbitrary component, to the mainmaterial of each of the cover material and intermediate layer material.Examples of such polymers may include a polyamide based elastomer, astyrene based block elastomer, a hydrogenated polybutadiene, and anethylene-vinyl acetate (EVA) copolymer.

The golf ball of the present invention, which is generally applied to atwo-piece solid golf ball or a multi-piece solid golf ball, can beproduced in accordance with a known process. While not particularlylimited, the two-piece solid golf ball can be produced by putting asolid core formed of the hot-molded product in a specificinjection-molding mold, and injecting the above cover material thereonby a specific known manner, and the multi-piece solid golf ball can beproduced by putting a solid core formed of the hot-molded product in aspecific injection-molding mold and sequentially injecting the aboveintermediate layer and cover material thereon by a specific manner.Alternatively, the cover material is formed on the solid core bypress-molding.

The thickness of the intermediate layer used for a multi-piece solidgolf ball may be in a range of 0.5 mm or more, preferably, 1.0 mm ormore, with the upper limit being in a range of 3.0 mm or less,preferably, 2.5 mm or less, more preferably, 2.0 mm or less, mostpreferably. 1.6 mm or less.

The thickness of the cover used for a two-piece solid golf ball ormulti-piece solid golf ball may be in a range of 0.7 mm or more,preferably, 1.0 mm or more, with the upper limit being in a range of 3.0mm or less, preferably, 2.5 mm or less, more preferably, 2.0 mm or less,most preferably, 1.6 mm or less.

The golf ball of the present invention can be produced with its diameterand weight specified under a golf rule for golf games. Concretely, thediameter of the golf ball can be set in a range of 42.67 mm or more,with the upper limit being in a range of 44.0 mm or less, preferably,43.5 mm or less, more preferably, 43.0 mm or less, and the weight of thegolf ball can be set in a range of 45.93 g or less, with the lower limitbeing in a range of 44.5 g or more, preferably, 45.0 g or more, morepreferably, 45.1 g or more, most preferably, 45.2 g or more.

EXAMPLE

The present invention will be more clearly understood by way of, whilenot limited thereto, the following examples and comparative examples.

Examples 1 to 7 and Comparative Examples 1 to 6

A rubber composition for a solid core was prepared by adding corematerials shown in Table 2 to 100 parts by mass of each of polybutadienecomponents obtained by mixing polybutadienes of the following kinds (1)to (7) having physical properties shown in Table 1 at each mixing ratioshown in Table 2, and a solid core was produced from the rubbercomposition. In Table 2, “Percumyl D” (sold by NOF CORPORATION) was usedas dicumyl peroxide, and “NOCRAK NS-6” (sold by Ouchi-Sinko ChemicalIndustrial Co., Ltd.) was used as an antioxidant.

Kinds of Polybutadienes

(1) polybutadiene: “BR01” (sold by JSR Co., Ltd.)

(2) polybutadiene: “BR11” (sold by JSR Co., Ltd.)

(3) polybutadiene: “UBE101” (sold by Ube Industries, Ltd.)

(4) polybutadiene: “BR18” (sold by JSR Co., Ltd.)

(5) polybutadiene: “HCBN-5 (trial grade)” (sold by JSR Co., Ltd.)

(6) polybutadiene: “HCBN-2 (trial grade)” (sold by JSR Co., Ltd.)

(7) polybutadiene: “HCBN-4 (trial grade)” (sold by JSR Co., Ltd.)

TABLE 1 Cis-1,4- Mooney Structure Viscosity Kind Catalyst (%) (ML) 20 ×ML − 600 η Polybutadiene (1) Ni 96 44 280 150 (2) Ni 96 44 280 270 (3)Co 95 38 160 130 (4) Ni 96 60 600 590 (5) Nd 96 42 240 150 (6) Nd 96 40200 280 (7) Nd 96 44 280 390

TABLE 2 Examples Comparative Examples Kind 1 2 3 4 5 6 7 1 2 3 4 5 6Polybutadiene Composition (mass %) (1) 50 40 50 50 50 (2) 20 50 40 50 50(3) 50 50 50 (4) 50 50 (5) 60 50 (6) 80 50 50 50 50 50 100 (7) 60 CoreComposition (parts by mass) Polybutadiene 100 100 100 100 100 100 100100 100 100 100 100 100 Dicumyl 1.4 1.4 1.4 1.4 1.4 1.4 1.4 1.4 1.4 1.41.4 1.4 1.4 Peroxide Zinc Oxide 22 22 22 22 22 22 34.5 22 22 22 22 2234.5 Antioxidant 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2Zinc Acrylate 24 24 24 24 24 24 24 24 24 24 24 24 24

The rubber composition for a solid core was then suitably kneaded by akneader or a roll, and the workability at the time of extruding aspecific amount of the rubber composition was evaluated under thefollowing criteria. The results are shown in Table 3.

Evaluation of Workability in Extrusion

The surface and shape of a slug obtained by extruding the rubbercomposition were evaluated under the following criteria:

Grade 5: the workability in extrusion is very good and the slug surfaceis good.

Grade 4: the workability in extrusion is good and the slug surface isslightly rough.

Grade 3: the rubber composition is extrudable but scuffing occurs on theslug surface.

Grade 2: the rubber composition is extrudable but scuffing on the slugsurface is very conspicuous.

Grade 1: A failure in shape of the slug occurs, and it is difficult toextrude a specific amount of the rubber composition.

In each of Examples 1 to 6 and Comparative Example 1 to 5, a solid corehaving a diameter of about 38.9 mm and a weight of about 36.0 g wasproduced by using the above rubber composition for a solid core, and ineach of Example 7 and Comparative Example 6, a solid core having adiameter of 35.3 mm and a weight of 31.0 g was produced by using theabove rubber composition.

The press-molding of the rubber composition was performed at 150° C. for20 min.

A deformed amount of the solid core thus obtained, measured by applyinga load of 980 N (100 kg) thereto, was examined, and further theresilience of the solid core was examined as follows. The results areshown in Table 3.

Flexural Amount (Load: 980 N)

A deformed amount (mm) of the solid core, measured by applying a load of980 N (100 kg), was measured.

Resilience

The initial velocity of a golf ball obtained by using the above solidcore was measured by an initial velocity meter of the same type as thatused in a certified institution USGA. For each of Examples 1 to 6 andComparative Examples 1 to 5, the resilience was expressed by adifferential initial velocity based on an initial velocity inComparative Example 4. For Example 7, the resilience was expressed by adifferential initial velocity based on an initial velocity ofComparative Example 6.

In each of Examples 1 to 6 and Comparative Examples 1 to 5, the solidcore was put in a specific mold, and a cover material (Himilan1601/Himilan 1557=50/50) was injection-molded thereon, to produce atwo-piece solid golf ball having a diameter of 42.7 mm and a weight of45.3 g. In each of Example 7 and Comparative Example 6, the solid corewas put in the same specific mold as described above and an intermediatelayer material (Himilan 1706/Himilan 1605=50/50) was injection-moldedthereon, to produced an intermediate layer covered core having adiameter of about 38.7 mm, and then the intermediate layer covered corewas shifted in a specific mold and a cover material (Himilan 1650/Surlyn8120=50/50) was injection-molded thereon, to produce a three-piece solidgolf ball having a diameter of about 42.7 mm and a weight of about 45.3g.

The carrying performance of each of the golf balls thus obtained wasexamined. The results are shown in Table 3.

Physical Properties of Golf Ball

Each golf ball was hit at a head speed of 45 m/s by a hitting machine onwhich a driver (W#1) was previously mounted, and the carry and totaldistance of the hit ball were measured.

As shown in Table 3, it was found that the golf ball of the presentinvention can exhibit excellent resilience.

TABLE 3 Examples Comparative Examples 1 2 3 4 5 6 7 1 2 3 4 5 6 SolidCore Flexural 3.4 3.5 3.5 3.6 3.5 3.5 3.1 3.3 3.4 3.6 3.7 3.7 3.3 Amount(mm) (load: 980 N) Resilience +0.6 +0.5 +0.4 +0.6 +0.4 +0.4 +0.5 +0.6+0.3 +0.4 0 0 0 (m/s) Workability 3 4 4 2 3 3 4 1 2 1 5 4 4 in ExtrusionPhysical Properties of Golf Ball (HS45) Carry (m) 213.3 213.1 213.0213.2 212.7 212.5 213.5 213.1 212.3 212.5 209.5 209.2 209.5 Total (m)226.9 226.8 226.8 226.9 226.4 226.2 227.3 226.7 225.7 226.0 223.3 223.0223.6

What is claimed is:
 1. A golf ball including, as a composing element, a hot-molded product obtained from a rubber composition, said rubber composition comprising: a main rubber containing 10 to 90 mass % of a polybutadiene (a); an unsaturated carboxylic acid and/or a metal salt thereof; and an organic peroxide; wherein said polybutadiene has 60% or more of cis-1,4-bonds; and letting a Mooney viscosity (ML₁₊₄(100° C.)) of said polybutadiene be ML and a viscosity of a toluene solution containing 5 mass % of said polybutadiene at 25° C. be η(mPa·s), ML and η satisfy a relationship of η≧20×ML−600, wherein said golf ball is either a one-piece golf ball or a golf ball including a solid core; and wherein said golf ball is a non-wound solid golf ball.
 2. A golf ball according to claim 1, wherein said polybutadiene component (a) is synthesized by using a rare earth element based catalyst.
 3. A golf ball according to claim 1, wherein said polybutadiene component (a) is synthesized by using a rare earth element based catalyst, and is then reacted with a terminal denaturant.
 4. A golf ball according to claim 1, wherein said main rubber contains, in addition to said polybutadiene component (a), 90 to 10 mass % of a polybutadiene (b) having a Mooney viscosity of 55 or less.
 5. A golf ball according to claim 1, wherein said main rubber contains 40 to 90 mass % of polybutadiene (a).
 6. A golf ball according to claim 1, wherein said main rubber contains 50 to 90 mass % of polybutadiene (a). 